source of Mg, Ti, and Mn in 304 SS 3

[fusitexa]

dear all,

recently we have a crack issue in our 304ss bar and large inclusions were found along the crack. the sample was prepared and tested with SEM/EDS. attached is two figures of the test results, pls. review. could anyone tell me what is the source of the Mg, Ti, Mn and the other elements in the inclusion and how to prevent it happening? looking for your reply and thanks.

 

[fusitexa]

another figure

 

[arunmrao]

Not knowing the process or product I am hazarding a guess, which may be inaccurate:

a) Mg source is refractory wear out from melting furnace.

b) Ti and Mn : Poor selection of charge mix . Ti and Mn containing charge must have been blended.

 

[jwhit]

Mn is usually an intentional addition. Type 321 scrap may have gone into the charge which accounts for Ti. Type 304 should be able to handle these two elements without issue as long as they aren't in exorbitant amounts. If the Mg source is from the refractory in the furnace I would suspect that is the cause of the inclusions and cracking, would expect that there are numerous other oxides in the inclusion. It may also come from returns (crops from billets etc.)going in to the furnace. Dirty material breeds dirty material.

 

[mrfailure]

When I see Ti, my brain usually takes me to paint as a possible source. Is that possible (it could also account for Al and Si)? Or is that thought just too goofy?

Aaron Tanzer

http://www.lehightesting.com

 

[arunmrao]

For Mn contamination I had 200 series of stainless steel on my mind. For stainless steel, I feel a more careful choice of raw materials and refractories is essential.

 

[EdStainless]

If we presume that they are oxides (not carbides or nitrides) then refractory is main source.
What is the product form? (plate, sheet, long product)
Was it continuously cast or ingot cast?
Is this near the surface or interior?
What was the hot reduction and cold reduction in forming?

I hate to say it but getting clean 304L and 316L is difficult. They are commodities and most mills treat them as such.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[TomDOT]

mrfailure: The common use for titanium in paint is titanium dioxide, the best white pigment around, becoming reasonably available after WWII. So, typically seen in topcoats and not the highest percentage of pigment since it is pricy. Aluminum is now less common in modern paint, but was used extensively as a topcoat for exterior steel (over a red lead primer.) Lots of filler pigments have silicon. Silica sand, talc, most clays and wollastonite are some which come to mind immediately.

 

[EdStainless]

You can also find Ti, Al, and Mg used as deoxidizers.
But if it is a large oxide inclusion I would suspect a piece of refractory.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mrfailure]

Piece of refractory does make better sense as Ed suggests based on the photomicrograph.

Aaron Tanzer

http://www.lehightesting.com

 

[TomDOT]

Makes more sense to me too - I just wanted to respond to your comments regarding elements in paint.

 

[TVP]

I'm not as familiar with refractory composition for SS vs. conventional carbon/alloy steels, but the Mg content seems too low to say that most of the item in question is from the refractory lining. The majority of the composition is Si, Cr, and Mn together with O. These are the elements that oxidize most easily, so I would surmise that this is predominantly oxidation products that were not effectively removed during the ladle treatment. There might be some refractory lining in this clump as well.

 

[mcguire]

There Cr, Mn, Si oxides are the products of the deoxidation process. They should form but better steel making techniques would have removed them. They formed in the molten steel and agglomerated, along with Al and Mg from the refractories. The fact that they are all together confirms that they came together in the molten state , from which they should have been removed. Bad practice.
The Ti may have been intentional, but we can never know for sure. Some steel makers add it to suppress hot workability problems. In this case, however, the steel maker doesn't look that sophisticated.
Arunmrao! I'm in Mumbai on April 21. Is that convenient for a visit?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[fusitexa]

guys,

thank you very much for your reply.
so far, i know a little about the process. what i know is the inclusion is in the center of the bar. and the bar's diameter is about 20mm; attached is another figure which you can see the full view of the inclusion, thanks again for you kindly reply.

 

[arunmrao]

@mcguire

I was just wondering if you would respond to the OP and what your response would be. Well, I have not been disappointed, you you have provided a very good insight. A star from me.

Making stainless steel products has been lowered to a commodity product,thus many factors are ignored. For me as a casting manufacturer,poor quality of stainless steel scrap has become a cause of concern.

I have responded on your FB account.